Method for casting blocks of metal



May I, 1934. ROTH 1,956,910

- METHOD FOR CASTING BLOCKS OF METAL Filed D80. 1, 1932 2 Sheets-Sheet, 1

In c-nTv-r 5M Po May 1, 1934. H 1,956,910

METHOD FOR CASTING BLOCKS OF METAL Filed Deo'. 1, 1932 2 Shets-Sheet. 2

Patented May 1, 1934 UNITED STATES PATENT OFFICE In Germany 2 Claims.

As is well known, the solidification stage is of primary importance as regards the properties and character of cast blocks ,of metal, particularly insofar as their further treatment by roll- 5 ing, drawing, pressing and the like is concerned.

All metals and metal alloys tend to a greater or less extent to form crystals on'passing from the fused liquid state into the solid state. This crystal formation has .a detrimental effect on the mechanical properties of the blocks, their density, rigidity, etc., and gives rise to the formation of gas filled cavities in the solid block, which is particularly inconvenient.

Consequently a large number of proposals have 5 been made which are intended to prevent the crystal formation or else to destroy the crystals which form, or to attain so fine a crystalline grain that it can be regarded as practically equivalent to a dense amorphous structure.

Among the methods operating in this direction with some success is the shaking of the mould or chill mould which is filled with the liquid metal, and this has been attempted in very. many different forms.

ature by auxiliary heating and shaken during this period.

It has also been proposed to effect the shaking motion in a direction transversely to the growth of the crystals over a temperature range which begins above the solidification temperature and terminates beneathit.

These endeavors and many others made in the same direction have, however, not yet led to a complete solution of the problem. The solidified metal blocks were not uniformly dense and above all were not freed from enclosures of foreign substances, particularly gases.

The present invention which is based on a very detailed study of the phenomena and operations which are fundamental in the shaking of solidifying cast metal blocks, is intended to overcome these difiiculties in their entirety and to ensure the production of a uniformly dense cast metal block which is practically free from enclosed foreign bodies.

In order that the nature of the present method maybe clearly explained, the processes which }.occur in the shaking of a mould or chill mould -'fllled with the fused liquid metal in the usual way will be briefly set out.

While the metal is being introduced into the mould crystal formation commences from the bottom and from the sides and proceeds towards Thus, for example, the metal bath has been retained somewhat above the solidification temper- July 12, .1932

the centre, and continues after the mould has been completely filled.

The crystals interweave in bundles'and rays substantially transversely to the longitudinal direction of the mould from. the periphery inwardly. So long as the metal is in the fused liquid state, the foreign components particularly the surprisingly large quantities of gases, are uniformly dissolved in the bath. It is only at the moment when, on attaining the solidification temperature, the transformation from the liquid to the solid state commences, that the gases are released from the dissolved state; naturally they fill the spaces which are formed between the solidifying crystals due to the contraction, i. e. they deposit on the grain surfaces and boundary surfaces of the structure in molecular bubbles which are in part extremely small. Now if a block which is undergoing this solidification process is shaken, then that not inconsiderable part which is transformed into solid crystals immediately the metal is introduced into the mould is entirely unaffected by the shaking.

The gases which are enclosed in the solidified part can thus no longer escape no matter how much one shakes the mould. It is only possible for them to escape beforethe final solidification of this portion has occurred.

In the case of the residual metal which is solidifying in the mould there is in itself the possibility of removing the gas. This, however, is counteracted by the fact that also in these parts the crystal formation occurs in directions transversely and obliquely to each other, and that the gas bubbles which escape from one crystal bounded space which is destroyed by the shaking are inevitably caught again at another point.

Also the proposal to maintain the metal somewhat above the solidification temperature during the shaking and then suddenly to allow the block to solidify cannot be adopted, because so long as the metal is liquid the gas is in no way released from solution. As is known, it is not possible to shake any gas whatever from a liquid metal bath.

The method of casting the metal blocks which resides in maintaining the metal bath in the completely fused state and in turning it offers a path which holds prospect of success. Here the filling operation is fundamentally separated from the solidification operation and the solidification gradually occurring from the periphery on pouring in the metal is prevented. After the turning the solidification occurs rapidly and solely from one side, namely, from the cooled base. Thus the crystals form parallel to each other and are all disposed in the same direction from bottom to top. If now the mould were shaken from the commencement of the solidification, i. e., after the turning has been effected, then the gas bubbles which are released can escape through the capillary passages extending from bottom to top and formed by the crystal structure, whereas the crystals which have been freed from cavities pack against each other and in this way a dense uniform structure should be obtained.

However, with the method which promises such goods results a surprising experience has resulted. After the blocks have been shaken with the requisite intensity of shaking, i. e., with the requisite frequency until solidification occurs, it is found that they have a non-uniform character insofar as at a definite and carrying distance from the base clearly defined half-moon shaped layers or sections occur with a structure which is altogether different from that of the remaining contents of the mould. The examination of such a block gives the impression that in these layers the connection between the individual small particles of matter has been disturbed. Now it must be borne in mind that the transition from the liquid to the solid state passes first through a dough-like condition and then through a crumbly condition. Particularly in this latter state, the very fine crystals formed by the shaking are for the greater part rigid, and still covered with a thin layer of liquid metal adapted to form the mutual connections. If on the other hand it is remembered that the intensity or frequency of shaking is adapted to the entire mass of the liquid bath, then it is seen immediately that this is too intensive and too strong for the reduction of the liquid portion of the metal which occurs with increasing solidification and that with this solidification an increasing shaking is applied to the structure which, instead of causing the fine crystals to grow together, occasions precisely the opposite.

The recogniton of this fact gave the rule forming the basis of the present invention, namely, that the intensity of the shaking, i. e., above all the frequency thereof must be adapted to the increasing solidification, and the shaking must be reduced in proportion to the decrease of the liquid portion of the bath.

In the drawings forming a part of this specifi cation:

Figure l is a view in section illustrating diagrammatically the mould and crucible employed in the casting operation intheir relative positions at the commencement of the pouring or casting operation.

Figure 2 illustrates the relative positions of the parts of Figure 1 after the mould has been completely filled with the molten metal and moved gradually during the pouring operation to the position illustrated.

Figure 3 is view in section of the mould of Figure 1 with a cover applied thereto.

Figure 4 is a view in section, similar to Figure 3, of the parts in cooling position, the cooling means being diagrammatically indicated.

Figure 5 is a view in elevation of a shaking or mould vibrating apparatus according to my invention.

Figure 6 is a top plan view of the shakin apparatus of Figure 5. i

It will be seen that the mould comprises a mould a, properly speaking, and a heating box or case b. The mould a is made of a suitable cast metal or alloy and is heated by any appropriate heating means provided in the box or case b of the said mould, to the temperaturerequired by the metal to be cast.

For the purpose of avoiding loss of heat by radiation the heating box b is enclosed in or surrounded by a heat-insulating jacket 0. Figure 1 shows the relative positions of the parts at the commencement of the casting operation, the mould adapted to be turned about the horizontal axis d occupying an inclined position towards the crucible e, in order to ensure a smooth pouring of the molten metal into the mould, while Figure 2 illustrates the relative positions of the parts after the mould has been completely filled with the molten metal and simultaneously moved gradually to horizontal position. The casting operation properly speaking thus is finished.

Subsequently a suitable top-piece, preferably in the form of a metallic plate I, is to be placed on the mould as shown in Figure 3 and tightly forced against the rim of the opening of the mould so as to form a tight closure, whereupon the mould is turned about the axis at by 180' as will be seen in Figure 4 and sprinkled with a suitable cooling liquid, a spraying pipe g, nozzles or the like being provided for the purpose as shown in Figure 4.

The metal may be poured into the chill mould according to British Patent 2841 or German Patents 290,833; 204,752; 232,468 and 239,565, and by turning the metal which was previously completely liquid according to United States Patent 1,850,477 it will be put into a state which is most suitable for the shaking.

The casting method as herein described involves the desirable result that the delivery or fiux of heat from the solidifying metal will not depend upon or be left to the chance of incident occurrences, but rather will take place exclusively in the direction towards the base so as to be adjustable with high accuracy to absolutely con-.

form to the particular solidifying properties of the metal to be cast.

Now if the cast block be allowed to solidify in the manner hereinbefore described, it would be found that the structure of the metal of any etched cross-sectional surface of the block would mainly exhibit a stalk-like configuration spreading from the cooled bottom surface, which involves the danger of the formation of small pipes between the stalks and the intrusion of gas into said pipes since, as is well known in the art, the gas will not be released prior to the moment of solidification so that in the subsequent rolling of the block for the production of sheets, band and the like the preparatory heating thereof to red-heat will result in the production of a product containing flaws.

Inorder to prevent or remedy this defect the chill mould is mounted upon a shaking apparatus which as shown in Figures 5 and 6, comprises a frame h preferably made of wrought iron and adapted to swing on legs 2 which, as illustrated, preferably comprise fiat leaf springs composed of a sumcient number of leaves to give the desired flexibility to permit frame h. to reciprocate in the most eifective manner. The reciprocatory movement of the frame h together with the chill mould a mounted thereon is brought about by means of a crank-gear driven by a motor m through the agency of a friction gearing l which will permit controlling and changing the frequency of the reciprocations or strokes 'within the required limits. Moreover, the crank pin of T the gearing k is adjustable so that the stroke or amplitude of the to and fro movements of frame h can be controlled and adjusted to conform to the required shaking frequencies. Obviously it goes without mentioning that the reciprocatory or shaking movement may just as well be accomplished with the aid of any other suitable machinery elements.

The chill mould is mounted on trunnions n supported in suitable bearings of the frame It so that it may be turned about the common axis of said trunnions. Any suitable driving means is provided for the purpose. I have indicated by reference character 3: a hand operated mechanism for rotating mould a about its axis passing through trunnions n. Mechanism p comprises a hand wheel q and suitable gearing to impart motion from pinion r on the hand wheel shaft to gear s.

Now, when the chill mould has been turned to the position shown in Figure 4 and subjected to the shaking treatment as required or preferred, the finished metal block will exhibit in any etched cross-sectional surface thereof a satisfactory dense structure of fine grain.

Amplitude and frequency of the strokes or reciprocations to be imparted to the mould obviously must be controlled and adjusted to conform to the particular physical properties of the batch of metal to be cast. Thus, for example in case of aluminium, it has been found that a block weighing 50 kg. and shaken by an amplitude of about 12 mm., first for 3 minutes at a frequency of 300 strokes, subsequently for 4 minutes at a frequency of 200 strokes and finally for 6 minutes at a frequency of 100 strokes per minute will have a structure and grain of unobjectionable character and of best quality for rolling purposes.

An essential feature of the invention resides in selecting the stroke or shaking intensity with relation to the still liquid condition of the metal in the mould. If a shaking motion of insufilcient intensity is applied or maintained, the metal of the block will display a stalky structure involving the risk of formation of flaws in the rolled product. On the other hand if the shaking intensity is excessive the metal of the gradually and progressively solidifying casting will be broken up so that fissures and similar defects will be provoked which can be readily detected on any etched cross-sectional surface of the finished block.

The following example will serve to illustrate the manner in which the invention can be carried into effect.

It is assumed that it is a case of the shaking of 500 kilogrammes of brass which has been poured into a chill mould in the manner previously described A shaking frequency 1120 per minute was found to give the optimum result ensuring a satisfactory breaking up of the crystals.

The time taken for complete solidification was found to be 28 minutes. Thus in the usual way shaking would be efiected at the above frequency for 28 minutes.

According to the invention the number of strokes is reduced in such a way that after 28 minutes it is practically zero.

This reduction should be effected continuously and gradually and may be effectively accom- At the same time the following consideration must also be taken into account. With increasing solidification the speed of cooling alters and in the portion which is still in the liquid state it is different from that in the portion which is already solid. Whereas it follows from the previous discussion that at the beginning of the solidification the heat is led away substantially only through the cooled base, with increasing solidification it also passes through the metal portions which have already solidified. In other words, the wall through which the heat passes is increasingly thicker with progressive solidification and consequently the transfer of heat is slower. It is clear that this variation in the rate of cooling must also be taken into account in the degree in which the speed is reduced in order to ensure the best results of the shaking operation.

Thus once the fundamental principle constituting the invention has been established, this modification of the shaking gear can be efiected directly from the consideration of and experience available to the expert, the final aim being to obtain a uniformly dense block free from gas.

Appropriate shaking as described will have not only a beneficial influence on the structure of the metal, but also will produce a marked refinement thereof. For example, a casting of aluminium containing according to analysis 0,0016 P, 0,006 V and 0,004 Ti had been shaken according to the present invention with an amplitude of about 6 mm. at a frequency of 700 strokes per minute and by way of analysis it has been found that the metal of the shaken block contained 0,2 P, 0,013 V and 0,012 Ti in the neighborhood of the toppiece. If such blocks are dipped into a water bath, after the shaking operation has been performed a vehement development of gases will set up in the said top-piece which no doubt is attributable to decomposition of impurities elim-. inated from the metal by the shaking operation.

In another case blocks of aluminium containing 0,11 per cent of titanium has been subjected to a shaking treatment of 1300 strokes at'an amplitude of about 2 mm. i

1. A method for casting blocks of metal consisting in shaking the mould containing the liquid metal during solidification of' the latter and diminishing intensity and frequency of the shaking motion in proportion to the progressing solidification.

2. A method for casting blocks of metal consisting in shaking the mould during solidification, diminishing intensity and frequency of the shaking motion in proportion to progressing solidification and modifying the decrease of the shaking in relation to the variation in the speed of cooling.

ERNST ROTH. 

